The invention relates to a circuit for frequency translation, and more particularly to a circuit for translating a useful or input signal with a heterodyne signal using the principle of quadrature signal processing in a modulator or demodulator.
In modern communications and position-finding systems, an evaluation by amount and phase frequently takes place in the receiver. For computation of the phase information, orthogonal splitting of the receiver signal into an in-phase branch (I) and a quadrature branch (Q) is necessary. A circuit unit generating the two quadrature signals by a complex mixture with subsequent low-pass filtration is designated a quadrature or vector demodulator.
Digitalizable baseband signals are mostly generated from an intermediate frequency signal using the quadrature demodulator. In principle, however, the received signal can be translated in one step from a high frequency signal to the baseband by means of coherent or asynchronous direct mixing.
In a corresponding manner, the principle of quadrature signal processing is applied to generate a transmission signal from a useful signal and from a heterodyne signal in a modulator. Circuits for modulators and demodulators can be constructed using identical principles as regards their substantial aspects.